Semiconductor technology is the key point of the information society. However, as technology developing, the traditional semiconductor material such as silicon (Si) could not meet the demand of the society. Therefore, the next generation semiconductor material silicon carbide (SiC) is widely concerned. Compared to Si, SiC has some superior physical and chemical properties. On the other hand, it is difficult to polish SiC wafers due to the chemical, mechanical, and thermal stability. To achieve high-efficient CMP processing of SiC substrates, oxygen gas was introduced which might increase removal rates. MnO2 slurry was selected instead of silica slurry and strong oxidant KMnO4 was used to improve SiC-CMP process as an additive. In this paper, the effect of oxidant was inspected first. Meanwhile, we carried out the CMP experiment with the new type CMP machine to control the processing atmospheres including types of gases and gas pressures. As conclusions, oxygen and high atmospheric pressure can increase the removal rate in MnO2 slurry. KMnO4 additive has a great effect on increase of the removal rate. One of additional interesting results is that there seems to be the optimum mixture ratio of N2 and O2 gases to achieve a higher removal rate of SiC wafer.